In the processing of various fabrics, particularly including but not limited to tubular and open width knitted fabrics, an integral part of many finishing operations performed on the fabric, to ready the fabric for cutting into garment sections, is the performance of lengthwise compressive shrinkage operations for stabilization of the fabric geometry. Knitted fabrics in particular, because of their construction, tend to be somewhat geometrically unstable. During normal processing of the fabric, to prepare it for the manufacture of garments, the fabric frequently is wet and under longitudinal tension. As a result, the fabric tends to become elongated lengthwise and narrowed widthwise. Accordingly, as a final step in the process of finishing the fabric and making it ready for cutting into garments, the fabric typically is laterally distended to a predetermined width, and then subjected to one or more mechanical compressive shrinkage operations in the lengthwise direction, such that the fabric, when later cut and sewn into garments, does not undergo significant dimensional change when worn and laundered.
Equipment for mechanical compressive shrinkage of knitted fabrics is in general known. A particularly advantageous form of apparatus for such purpose is described in the Milligan U.S. Pat. No. 4,882,819, owned by Tubular Textile Machinery. This equipment comprises a pair of controllably driven rollers, one a feed roller and the other a retarding roller. An arcuate shoe is associated with the feed roller and forms a confined path to guide fabric, being advanced by the feed roller, toward and into a compressive shrinkage zone formed by opposed blades projecting between the feed and retarding roller. The blades define a short, confined path for guiding the fabric as it traverses from the surface of the feed roller to the surface of the retarding roller. The retarding roller is driven to have a surface speed slightly less than that of the feed roller, so that the fabric is controllably compacted in a lengthwise direction, principally in the short confined path defined by the opposed blades.
Compressive shrinkage equipment of the general type described above must be manufactured, maintained and operated with very fine, accurately controlled clearances. Particularly in machines designed to process wide fabrics, maintaining of the necessary fine tolerances during operations has presented problems, partly because of the necessity for operating the equipment with the active components at significantly elevated temperatures. In the past, for heating the feed roll, it has been common to utilize steam, directed internally of the feed roll. For heating of the upper shoe and the blade associated therewith, it has been common to utilize electrical heating elements, such as Calrods. Both the steam and the electrical heating arrangements have significant shortcomings, in that it is necessary to cycle on and off the flow of steam and the flow of electrical energy, in order to avoid overheating of the components. This tends to result in an excessive cycling of the component temperatures between upper and lower limits, causing undesirable variations in the expansion and contraction of the components. Additionally, when it is necessary to stop the machinery for changing of a fabric batch or for other reason, it is typically necessary to shut off the flow of steam to the feed roll altogether, and this can result in condensation forming within the hollow interior of the feed roll. As a result, there can be a substantial difference in temperature between the bottom and the top of the roll, which may cause bowing of the roll for a period of time when the equipment is restarted. This can result in interference and damage to the finely adjusted components.
Several steps have been taken in an effort to overcome the disadvantages of utilizing steam for heating of the feed roll. One of these is the utilization of circulating hot oil, which is heated remotely from the feed roller, by means of a steam-heated heat exchanger. A system of this type minimizes cycling and eliminates the problems that otherwise arose from the condensation of steam during down periods. The use of circulating oil, however, has important disadvantages. With any fluid system it is necessary to utilize rotary joints to supply the medium to a rotating roller, and such joints can sometimes be a source of leakage. More importantly, perhaps, it is necessary from time to time to service and/or exchange the feed rollers, and at such times a circulating oil system is messy and difficult to deal with, particularly in an environment in which cleanliness of the equipment is important so as not to stain the fabric being processed.
Attempts have also been made to utilize heated water, instead of oil, circulating through the feed roller and heated externally thereof by a steam-fed heat exchanger. While this solved certain problems encountered with the circulation of heated oil through the feed roller, it is necessary, in order to achieve desired levels of operating temperatures over a wide range of production operations, to maintain the circulating water under significantly elevated pressure, as much as 40 to 50 psi in order to operate at desired temperatures. Additionally, both the oil and water systems retained the known electrical heating arrangements for the upper shoe assembly.
Pursuant to the invention, a novel and improved heating system is provided for a mechanical compressive shrinkage apparatus, in which a circulating liquid medium is employed, circulating in series through a plurality of components required to be heated, including the upper shoe assembly, the feed roller and a lower shoe assembly which mounts the lower blade element. Significant advantages are derived from flowing the fluid medium in series through these several components.
By directing flow of the heating medium in series, preferably through the upper shoe first, then the feed roller and finally the lower shoe, all of these precisely adjusted and mechanically cooperating elements of the compactor station are maintained in a steady and uniform temperature relationship while the equipment is in operation, and also while it is stopped. The equipment can be started from a cold condition more easily and reliably, and also more easily restarted from a temporarily stopped condition. By reliably assuring controlled and uniform heating of the several components, it is significantly less likely that expensive, precision components will be damaged by reason of temporary thermal distortions.
Pursuant to another aspect of the invention, the heated liquid medium is in the form of a mixture of water and a harmless "anti-freeze" additive, such as propylene glycol alcohol (PGA), which enables the system to operate throughout the desired temperature ranges without requiring excessive pressures to be employed. For example, with a mixture of about 70% water and 30% PGA, the liquid medium may be heated to temperatures of 230.degree. F. at pressures on the order of 15-30 psi, a much more easily handled pressure level than with water alone, which would involve 40-50 psi. Unlike the circulating hot oil, moreover, the water/PGA mixture does not present a significant cleanup problem when machine maintenance is required.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments of the invention and to the accompanying drawings.